Most of your questions are covered in the familiarisation booklet which you can find on Warwickshire’s website here:
https://www.warwickshire.gov.uk/elevenplusLook on the right hand side for a link to the booklet.
You can normally not go back once you have left a section and moved onto the next timed section. There is normally a break between the two 1 hour sessions. I suggest to send her in with a snack for the break.
One thing I learnt is to focus on my dd’s best working speed and remind her it is about working at her best working speed, not so fast she makes silly mistakes or panic.
I have just been through this for the second time and am happy to answer any questions if I can.